In recent years, an amount of data which is processed on a computer system has been increased more and more, and it is necessary to process enormous data at high speed. In accordance therewith, it is necessary to further increase a communication speed between a computer and an I/O device. It is also necessary to further accelerate a speed of a computer which controls transmission/reception of data to and from an I/O device.
A computer in an open system widely uses Host Bus Adapter (HBA) which uses a Peripheral Component Interconnect (PCI) bus which is decided at PCI-SIG for connecting to CPU or a main storage at inside of a computer. Also, HBA which uses a further accelerated Express (R) bus (PCIe bus) is widely used in place of a PCI bus.